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// Copyright 2010 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build darwin freebsd linux netbsd openbsd

// Unix environment variables.

package syscall

import "sync"

var (
        // envOnce guards initialization by copyenv, which populates env.
        envOnce sync.Once

        // envLock guards env and envs.
        envLock sync.RWMutex

        // env maps from an environment variable to its first occurrence in envs.
        env map[string]int

        // envs is provided by the runtime. elements are expected to be
        // of the form "key=value".
        Envs []string
)

// setenv_c is provided by the runtime, but is a no-op if cgo isn't
// loaded.
func setenv_c(k, v string)

func copyenv() {
        env = make(map[string]int)
        for i, s := range Envs {
                for j := 0; j < len(s); j++ {
                        if s[j] == '=' {
                                key := s[:j]
                                if _, ok := env[key]; !ok {
                                        env[key] = i
                                }
                                break
                        }
                }
        }
}

func Getenv(key string) (value string, found bool) {
        envOnce.Do(copyenv)
        if len(key) == 0 {
                return "", false
        }

        envLock.RLock()
        defer envLock.RUnlock()

        i, ok := env[key]
        if !ok {
                return "", false
        }
        s := Envs[i]
        for i := 0; i < len(s); i++ {
                if s[i] == '=' {
                        return s[i+1:], true
                }
        }
        return "", false
}

func Setenv(key, value string) error {
        envOnce.Do(copyenv)
        if len(key) == 0 {
                return EINVAL
        }

        envLock.Lock()
        defer envLock.Unlock()

        i, ok := env[key]
        kv := key + "=" + value
        if ok {
                Envs[i] = kv
        } else {
                i = len(Envs)
                Envs = append(Envs, kv)
        }
        env[key] = i
        setenv_c(key, value)
        return nil
}

func Clearenv() {
        envOnce.Do(copyenv) // prevent copyenv in Getenv/Setenv

        envLock.Lock()
        defer envLock.Unlock()

        env = make(map[string]int)
        Envs = []string{}
        // TODO(bradfitz): pass through to C
}

func Environ() []string {
        envOnce.Do(copyenv)
        envLock.RLock()
        defer envLock.RUnlock()
        a := make([]string, len(Envs))
        copy(a, Envs)
        return a
}